Field
This disclosure relates generally to components for medical circuits, and in particular to components for medical circuits providing humidified gases to and/or removing humidified gases from a patient, such as in positive airway pressure (PAP), respirator, anaesthesia, ventilator, and insufflation systems.
Description of the Related Art
In medical applications, various components transport gases having high levels of relative humidity to and from patients. Condensation, or “rain out,” can be a problem when the high humidity gases come into contact with the walls of a component at a lower temperature. However, condensation is dependent on many factors, including not only the temperature profile in the component, but also the gas flow rate, component geometry, and the intrinsic “breathability” of the material used to form the component, that is the ability of the material to transmit water vapor, while substantially resisting the bulk flow of liquid water and the bulk flow of gas.
For example, PAP systems (ventilation systems that provide patients with breathing gases at positive pressure) use breathing tubes for delivering and removing inspiratory and expiratory gases. In these applications, and in other breathing applications such as assisted breathing, the gases inhaled by a patient are usually delivered through an inspiratory tube at humidity near saturation. The breathing gases exhaled by a patient flow through an expiratory breathing tube and are usually fully saturated. Condensation may form on the interior walls of a breathing circuit component during patient inhalation, and significant condensation levels may form during patient exhalation. Such condensation is particularly deleterious when it is in close proximity to the patient. For instance, mobile condensate forming in a breathing tube (either inspiratory or expiratory) can be breathed or inhaled by a patient and may lead to coughing fits or other discomfort.
As another example, insufflation systems also deliver and remove humidified gases. During laparoscopic surgery with insufflation, it may be desirable for the insufflation gas (commonly CO2) to be humidified before being passed into the abdominal cavity. This can help prevent “drying out” of the patient's internal organs, and can decrease the amount of time needed for recovery from surgery. Even when dry insufflation gas is employed, the gas can become saturated as it picks up moisture from the patient's body cavity. The moisture in the gases tends to condense out onto the walls of the discharge limb or tube of the insufflation system. The water vapor can also condense on other components of the insufflation system such as filters. Any vapor condensing on the filter and run-off along the limbs (inlet or exhaust) from moisture is highly undesirable. For example, water that has condensed on the walls can saturate the filter and cause it to become blocked. This potentially causes an increase in back pressure and hinders the ability of the system to clear smoke. Further, liquid water in the limbs can run into other connected equipment, which is undesirable.
Attempts have been made to reduce the adverse effects of condensation by incorporating highly “breathable” materials—that is, materials that are highly permeable to water vapor and substantially impermeable to liquid water and the bulk flow of gases—into the tube walls. However, this has required extremely thin membrane walls in order to achieve breathability sufficiently high to prevent or reduce condensation. As a result, tubes having acceptable breathability have had wall thicknesses so thin that the tubes need significant reinforcing measures. These reinforcing measures add time, cost, and complexity to the manufacturing process. Accordingly, a need remains for breathable, yet strong, components for medical circuits for delivering humidified gases.